1. Field of the Invention
The present invention relates to an airbag apparatus including an airbag whose internal pressure upon inflation is controllable.
2. Description of Related Art
An airbag apparatus is known from JP2000-43672: the apparatus has an airbag provided with an exhaust hole for discharging part of inflation gas and a flap element for openably closing off the exhaust hole. The flap element is joined to an open/close mechanism that controls opening and closing of the exhaust hole in accordance with the seating position and physical size of an occupant such that the internal pressure of the airbag is controlled upon inflation.
In the above airbag apparatus, the flap element is formed of a flexible sheet-shaped member sized to close off the exhaust hole and is sewn to a periphery of the exhaust hole by a generally annular sewn seam by sewing thread formed all around the exhaust hole. The flap element is adapted to keep closing the exhaust hole when the airbag inflates with the flap member released from the open/close mechanism. When the airbag inflates with the flap member engaged by the open/close mechanism, the flap element is subjected to movement restriction by the open/close mechanism and is removed from the periphery of the exhaust hole by tearing out of the sewing thread of the sewn seam and thereby opening up the exhaust hole.
However, in the conventional art, the sewn seam that sews up the flap element to the periphery of the exhaust hole is formed into a generally annular contour. In other words, the sewn seam has a wide configuration that is generally orthogonal to the working direction of a tension applied to the sewn seam when subjected to the movement restriction by the open-close mechanism. Since the tension works on the wide sewn seam at one time, the sewing thread sometimes fails to tear out smoothly, so that the flap member is not removed quickly to uncover the exhaust hole.